In this webinar, participants can learn the accuracy of the Lattice-Boltzmann Method (LBM) solver for pedestrian wind comfort, by following along with the results in the simulation project: https://www.simscale.com/projects/ananthu_ajit/aij-_case_e_-_lbm_validation/ Users will be able to see the benefits of using a transient solver for pedestrian-level wind analyses, and ask additional questions in the live ‘Q and A’. The project uses experimental results from the Architectural Institute of Japan to validate computational fluid dynamics (CFD) findings. The case being validated is Case E, which consists of a complex of buildings with simplified geometry. The aim of the simulation is to reproduce the macro-level wind regime around the buildings by testing 4 wind directions, and to validate results from SimScale against the AIJ experimental results. Video: https://www.youtube.com/watch?v=d-9_nc_PefM You can access the slides here: https://www.slideshare.net/SimScale Learn more about CFD with SimScale: https://www.simscale.com/ Take a look at our dedicated page for upcoming webinars: https://www.simscale.com/webinars-workshops/ Make sure you subscribe to our YouTube channel to watch all of our webinars and more!

1. LATTICE-BOLTZMANN SOLVER VALIDATION
FOR PEDESTRIAN WIND COMFORT
DARREN LYNCH

2. DARREN LYNCH
CFD Application Engineer
Experienced in CFD and engineering design,
Darren studied Aerospace Engineering at
Brunel University and is part of the
Application Engineering team at SimScale.

3. 1. Benefits of Using Simulation
2. Introduction to SimScale
3. Today's Topic: Pedestrian Wind Comfort
4. Live Demonstration
5. Results Summary
6. Q & A

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11. LATTICE-BOLTZMANN SOLVER VALIDATION
OVERVIEW
To obtain highly accurate results for
pedestrian wind comfort, it is necessary
to perform a validation case and to
understand the setup used to obtain
valid results.
From here, findings and outcomes can
be used to set up simulations where a
high level of trust exists.

12. AIJ - ARCHITECTURAL INSTITUTE OF JAPAN
OVERVIEW
The AIJ publish a series of validation
cases to be used to test solvers
specifically in the pedestrian wind
comfort application and range in
complexity.
AIJ Case E consists of simplified building
shapes in building complexes, where the
city was based upon an area in Niigata,
Japan.

13. PEDESTRIAN WIND COMFORT
OVERVIEW
Pedestrian wind comfort is a function of
mean velocity, and therefore, the data
presented by the AIJ cases are
normalized velocities at listed point
locations at pedestrian level.
We can also explore the transient data
obtained in the simulation to understand
how other factors such as gusts would
affect pedestrians.

14. BACKGROUND

15. LATTICE BOLTZMANN METHOD
Lattice Boltzmann Methods (LBM)
are CFD algorithms which use
collision theories to predict the fluid
behavior.
Some advantages are:
● Less computational time
● Less computational power
● Simple and easy procedure
● Robust (handles bad geometry
well)
● Transient phenomena

16. TEST CASE: AIJ CASE E
OBJECTIVES
● Simulate wind through Niigata
city after a proposed
construction.
● Compare CFD results to those
obtained in an atmospheric
boundary layer wind tunnel and
assess the accuracy of CFD
results.
● Understand the sensitive setting
to obtain accurate results.
● Analyse the probe signals for
further significant findings.

17. ATMOSPHERIC BOUNDARY LAYER
● Accurate specification of the boundary
layer wind profile is crucial in correctly
simulating the pedestrian level wind
environment.
● The ABL, Velocity and Turbulence
profiles given by AIJ were applied via
tabular CSV input.

20. NORTH WIND DIRECTION
Wind Direction
-North
Comparison of Wind - Tunnel results with SimScale Lattice Boltzmann solver for Pedestrian
Wind Comfort Scenario.
Transient Velocity Plot from SimScale

21. NORTH WIND DIRECTION
Pearson’s Coefficient: 0.70
Statistically Averaged Velocity Plot from SimScale

22. SOUTH WIND DIRECTION
Wind Direction
-South
Comparison of Wind - Tunnel results with SimScale Lattice Boltzmann solver for Pedestrian
Wind Comfort Scenario.
Transient Velocity Plot from SimScale

23. SOUTH WIND DIRECTION
Pearson’s Coefficient: 0.79
Statistically Averaged Velocity Plot from SimScale

24. EAST WIND DIRECTION
Wind Direction
-East
Comparison of Wind - Tunnel results with SimScale Lattice Boltzmann solver for Pedestrian
Wind Comfort Scenario. Transient Velocity Plot from SimScale

25. EAST WIND DIRECTION
Pearson’s Coefficient: 0.86
Statistically Averaged Velocity Plot from SimScale

26. WEST WIND DIRECTION
Wind Direction
-West
Comparison of Wind - Tunnel results with SimScale Lattice Boltzmann solver for Pedestrian
Wind Comfort Scenario.
Transient Velocity Plot from SimScale

27. WEST WIND DIRECTION
Pearson’s Coefficient: 0.81
Statistically Averaged Velocity Plot from SimScale

28. DETAILED VELOCITY - EAST WIND DIRECTION
Consistent
High Velocities
Strong
Fluctuations
Consistent Low
Velocities

29. DETAILED VELOCITY - EAST WIND DIRECTION
● Signal analysis is possible by
downloading the probe plot data
directly from simscale.
● Here the signals were analysed and
compared to the standard deviations
around the mean value, and where the
maximum and minimum velocity
values lay.

30. OPENFOAM COMPARISON - TREND LINE
East Wind Direction -
openFOAM comparison
Wind Direction
-East
Comparison of Wind - Tunnel results with SimScale Lattice Boltzmann solver for Pedestrian
Wind Comfort Scenario.
Transient Velocity Plot from SimScale

31. OPENFOAM COMPARISON - LINEAR CORRELATIONS
East Wind Direction
Statistically Averaged Velocity Plot from SimScale

32. OPENFOAM COMPARISON - TABLE
SimScale
LBM
Simscale
openFOAM
Accuracy (R²) 0.739 0.717
Speed 10 hrs 70 hrs
Mesh Size 98
million*
30.3 million
Mean Results Yes Yes
Time Dependent
Results
Yes** No
Point signals Yes** No
*Lattice cells are different to FVM cells
**No validation results available or presented

33. AIJ CASE E - VALIDATION SUMMARY
● Although the mesh size was larger LBM,
it ran 7x faster than steady state
openFOAM
● LBM was slightly more accurate in all
tested directions
● Transient results are available,
however, transient data is available to
validate against in this case